In a conventional cluster tool, processing residual periods for wafers which are being processed at present in process chambers are calculated respectively, and selection of a wafer to be taken out of a load port is made in such a manner that the next wafer is transferred to a process chamber having the shortest processing residual period.
However, in a cluster tool provided with load lock chambers, transfer to each of the process chambers is performed via the load lock chamber. In the load lock chamber, a wafer is delivered between a loader module and the load lock chamber and a wafer is delivered between the load lock chamber and the process chamber, and therefore supply and exhaust of air responding to the degree of vacuum in the loader module or the process chamber are repeated. For this reason, selection of a wafer to be taken out of the load port in consideration only of the processing residual period in the process chamber may rather increase a delay in transfer because there occurs waiting for transfer due to processing such as supply or exhaust of air in the load lock chamber.
Further, in the case in which transfers of wafers having different recipe execution periods are performed, when selection of a wafer is made in consideration only of their processing residual periods, a transfer of one having a shorter recipe execution period may be kept waiting, bringing about a problem that the throughput as a whole system is decreased.